Goodwill and Other Intangible Assets - Other Intangible Assets (Details) - USD ($)	9 Months Ended
Jun. 30, 2020	Sep. 30, 2019
Other intangible assets
Amortized intangible assets, carrying amount	$ 790,200,000	$ 453,500,000
Amortized intangible assets, accumulated amortization	343,200,000	303,100,000
Amortized intangible assets, net	447,000,000.0	150,400,000
Total, carrying amount	833,900,000	497,200,000
Total, net	490,700,000	194,100,000
Goodwill and Other Intangible Assets (Textual) [Abstract]
Estimated amortization expense in 2020	50,500,000
Estimated amortization expense in 2021	53,500,000
Estimated amortization expense in 2022	50,600,000
Estimated amortization expense in 2023	49,400,000
Estimated amortization expense in 2024	46,400,000
Asset impairment charges	0
Trademarks
Indefinite-lived Intangible Assets [Line Items]
Allen-Bradley® trademark not subject to amortization	43,700,000	43,700,000
Computer software products
Other intangible assets
Amortized intangible assets, carrying amount	192,300,000	190,600,000
Amortized intangible assets, accumulated amortization	135,900,000	128,300,000
Amortized intangible assets, net	56,400,000	62,300,000
Customer relationships
Other intangible assets
Amortized intangible assets, carrying amount	348,500,000	110,500,000
Amortized intangible assets, accumulated amortization	85,000,000.0	69,200,000
Amortized intangible assets, net	263,500,000	41,300,000
Technology
Other intangible assets
Amortized intangible assets, carrying amount	164,500,000	110,400,000
Amortized intangible assets, accumulated amortization	79,500,000	69,500,000
Amortized intangible assets, net	85,000,000.0	40,900,000
Trademarks
Other intangible assets
Amortized intangible assets, carrying amount	70,900,000	31,400,000
Amortized intangible assets, accumulated amortization	29,500,000	26,400,000
Amortized intangible assets, net	41,400,000	5,000,000.0
Other
Other intangible assets
Amortized intangible assets, carrying amount	14,000,000.0	10,600,000
Amortized intangible assets, accumulated amortization	13,300,000	9,700,000
Amortized intangible assets, net	$ 700,000	$ 900,000

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized in the remainder of the fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 340
-Section 50
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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Total loss recognized during the period from the impairment of goodwill plus the loss recognized in the period resulting from the impairment of the carrying amount of intangible assets, other than goodwill.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit.

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Amount before accumulated amortization of intangible assets, excluding goodwill.

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Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges.

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